The dynamics and control of in-situ combustion.
Improved oil recovery (lOR) techniques target the 60% of oil left behind by primary
and secondary methods (those that utilise the natural energy of an oil reservoir). Air
injection in situ combustion (lSC) is a thermal lOR technique used in general to
increase the temperature in a reservoir and in turn reduce the viscosity of the oil. This
increases the mobility of the oil and can lead to significant improvement in recovery
factors. The process is complex and much work is needed to improve modeling
capabilities essential for reservoir management.
To investigate high pressure air injection a combustion tube facility has been
commissioned and four in situ combustion tube tests completed. This involved the
development of data acquisition and control software (lsc View) to fully automate the
air injection facility. The ISC tests were carried out with a West Shetland Clair crude
oil of 19.7°API and air injection fluxes between 12 and 70m3/m2hr and pressures
between 50 and 100 bar. Post-mortem analysis of the burned cores showed 100% oil
displacement in areas of core swept by the combustion front. In these areas the amount
fuel burned varied between 4.6 and 15.3 %OOIP (original oil in place). The
combustion front temperatures varied between 450°C and 730°C. It was found that
combustion front temperature increased with air injection flux. The combustion front
velocity varied between 10.4 and 22.2cmlhr. The combustion front velocity was
observed to increase with pressure thus the combustion front velocity and hence
propagation of the combustion front was shown to be reaction rate dependent.
History matching of the ISC tests was completed using the STARS simulator
(Computer Modeling Group) a fully implicit non isothermal reservoir simulator. The
simulations showed that when the grid size approached that of the actual reaction zone
then the kinetics at different pressures did not change. Therefore, at this grid scale, the
kinetic parameters used for a pseudo component representation of the oil can be
applied as if it were a pure component, independent of pressure.